Heat exchanger

ABSTRACT

An improved heat exchanger includes an integral side piece/end cap structure for closing the ends of tanks and providing a side piece for each side of the heat exchanger and includes connecting strands between an end cap section and a side piece section that are weak, allowing the breakage thereof prior to excessive thermal stresses being placed on tube to the header joints. Also disclosed is the use of clips on end cap section and/or tank ends together with a tab on the end cap section which may be used to self-fixture of the components during assembly.

FIELD OF THE INVENTION

This invention relates to a heat exchanger, and more particularly, to aheat exchanger whose components are assembled to one another bysoldering or brazing, for example, aluminum heat exchangers.

BACKGROUND OF THE INVENTION

Heat exchangers for vehicles as, for example, radiators or charge aircoolers, conventionally include a plurality of parallel, spaced, flattubes that extend between header plates with tube slots which sealinglyreceive the ends of the flat tubes. Serpentine fins are disposed betweenadjacent ones of the tubes and collecting tanks are assembled in sealedrelation to header plates on sides thereof opposite the tubes. As istypical with the heat exchangers utilizing the serpentine fins, tofacilitate assembly, side pieces are located along each side of the heatexchanger core and extend between corresponding ends of the two headersto sandwich a serpentine fin against an endmost tube in the core.Frequently, the heat exchangers are made from aluminum in whichappropriate part surfaces are clad with a braze alloy to allow thecomponents to be assembled together by a brazing process. It is likewisepossible to make copper or copper/brass heat exchangers using solder inlieu of a braze alloy.

It has been proposed in German patent application No. DE 102 37 769.3 tomake the tanks of such heat exchangers out of channel-like material.Closure caps are fitted to the ends of the tanks and the same may beformed separately or integrally with the side pieces. For example, oneside piece may have two closure caps formed thereon, one on each end ofthe side piece, to be fitted to the tank end at the corresponding end ofeach header plate.

A typical problem that occurs in the production of such heat exchangersis that the heat exchanger must be assembled from its individual partsin preparation for brazing or soldering. This means constituents must betemporarily fastened until the joining process is completed. Currently,various fixtures or jigs are used for the purpose and clamp the heatexchanger in assembled relation. The heat exchanger remains clampeduntil the soldering or brazing process is completed.

In order to minimize or eliminate the need for such fixtures, there havebeen proposed various expedients whereby parts of the heat exchangeritself are provided with integral fastening devices which eliminate oneor more fixtures or jigs. By way of example, reference is made to U.S.Pat. No. 6,131,286 dated Oct. 17, 2000 which discloses a tab and slitinstruction for temporarily holding two metal pieces together during ajoining process. This type of pre-assembly fastening is problematical inthe fabrication of heat exchangers because of the required slit. In heatexchangers, the slit and the protrusion must be joined absolutelytightly or else the heat exchanger will leak.

In addition, so-called “thermal cycling” that occurs during theoperation of heat exchangers, often leads to breaks. Thermal cyclingoccurs, for example, in a vehicle when the engine is operating when theheat exchanger runs at relatively high temperature and when the engineis turned off, the heat exchanger cools to ambient temperature.Temperature gradients also lead to the same problem. Even in operationwith the heat-exchange fluids at constant pressures, the side pieces inheat exchangers and the endmost tubes in the core tend to run coolerthan those in the center of the core.

In either event, thermal stresses arise and typically are concentratedat the tube to header joints. Of course, if the thermal stress leads tocracks at tube to header joints, the heat exchanger begins to leak andfrequently will require some sort of repair which can be expensive andwhich can lead to extensive down time for the apparatus with which theheat exchanger is used.

The present invention is directed to solving one or more of the aboveproblems.

SUMMARY OF THE INVENTION

It is the principal object of the invention to provide a new andimproved heat exchanger. More specifically, one object of the inventionis to provide a heat exchanger that may be readily manufactured withlittle or no use of jigs or fixtures in the pre-assembly process.

It is also a principal object of the invention to provide a heatexchanger that is less susceptible to failure or leakage due to thermalcycling or thermal gradients.

An exemplary embodiment of the invention achieves the foregoing objectsin heat exchangers that include a pair of parallel headers, each havingspaced tube slots aligned with tube slots in the other header. Tubesextend between aligned ones of the tube slots in the headers and finsextend between the tubes. Side pieces on opposed sides of the heatexchanger embrace the fins thereat and extend substantially between thecorresponding ends of the headers. A pair of channel-tanks, one for eachheader, is fitted to the corresponding header oppositely of the tubesand end caps having bent edges embracingly and sealingly closingopposite ends of each tank are provided. The end caps are integralextensions of each end of each side piece to form end cap/side pieces.The heat exchanger is characterized by a reduction in cross section ofeach end cap/side piece adjacent each end of each header of at leastabout 50%. Each such reduction is defined by at least one cutoutadjacent each end of each header.

In a preferred embodiment, fasteners are provided for securing the endcaps to the tank ends during assembly of the heat exchanger.

In a highly preferred embodiment, each of the cross section reductionsis at least about 80% of the cross section, and the end caps and sidepieces remain integral about the cutout or cutouts through the retentionof a connecting strand or a small number of connecting strands extendingacross the cutout(s) from the side piece to the integral end cap at eachend of each side piece.

In one embodiment, the heat exchanger is formed of aluminum and isassembled by brazing. The connecting strand or strands are sized to bereadily severed if necessary.

In a preferred embodiment, the fasteners include resilient, U-shapedclips on the end cap bent edge or on the ends of the tanks. Preferably,the clips are integrally formed of projections on the components.

In a preferred embodiment, the fasteners also include a tab on each endcap which is bendable to overlie an adjacent end of the tank.

In one embodiment, the U-shaped clips each include a sloped extremity onat least one of the legs thereon to serve as a pilot surface for receiptof a corresponding end of the tank or a corresponding bent edge of theend caps.

In one embodiment, the cutout(s) defines a central connecting strandextending between each side piece and the associated end cap, while inanother embodiment, the cutout(s) defines two spaced, off-centerconnecting strands extending between each side piece and the associatedend caps.

Other objects and advantages will become apparent from the followingspecification taken in connection with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary, perspective view of a side piece for a heatexchanger made according to the invention;

FIG. 2 is a view similar to FIG. 1, but of a modified embodiment;

FIG. 3 is similar to FIGS. 1 and 2, but illustrates a third embodiment;

FIG. 4 is similar to FIGS. 1-3, inclusive, but illustrates a fourthembodiment;

FIG. 5 is an enlarged, fragmentary view of one corner of a heatexchanger;

FIG. 6 is a side elevation taken from the left of FIG. 5;

FIG. 7 is a fragmentary sectional view taken approximately along theline 7-7 in FIG. 5;

FIG. 8 is a sectional view taken approximately along the line 8-8 inFIG. 5;

FIG. 9 is a vertical section of the structure shown in FIG. 5;

FIG. 10 is an exploded view of the structure of FIG. 5;

FIG. 11 is a view similar to FIG. 10 but of a modified embodiment of theinvention;

FIG. 12 is a fragmentary, elevational view of a corner of a heatexchanger made according to the invention;

FIG. 13 is a sectional view taken approximately along the line 13-13 inFIG. 12; and

FIG. 14 is a sectional view taken approximately along the line 14-14 inFIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As alluded to previously, the heat exchanger of the present invention isideally suited for vehicular use as, for example, a vehicular radiatoror charge air cooler. However, no limitation to vehicular use, or to aradiator, or charge air cooler is intended because those skilled in theart will recognize that the heat exchanger of the invention may be usedin a variety of environments and for a variety of purposes. For example,the same could be utilized in a heating system for a building, or thelike. In any event, no limitation to a particular environment of use orto a particular use is intended except insofar as expressly stated inthe appended claims.

With the foregoing in mind, several embodiments of the invention willnow be described.

Turning first to FIGS. 8, 9, and 10, a typical heat exchanger embodyingthe invention is shown fragmentarily. The same includes two, spaced,parallel header plates 20 (only one of which is shown) having upturnedside edges 22 along its length. Elongated tube slots 24 extendtransversely to the length of each header plate 20 from end to endthereof, and in turn receive the ends 26 of a plurality of flattenedtubes 28 which extend between corresponding tube slots 24 in the twoheaders.

An open-ended, open-bottomed channel-like tank, generally designated 30,includes a base 32 with depending sides 34. The sides 34 extend aboutthe remote surfaces of the flanges 22 as well as about the bent edge 36of an end cap part 38 of a combination side piece/end cap construction,generally designated 40. One or more ports 42 will be located in thetank, typically in one of the sides 34, for connection into the systemwith which the heat exchanger is used.

As seen in FIGS. 9 and 10, the side piece/end cap assembly 40 includesan end piece section 44 in addition to the end cap section 38. Asperhaps best viewed in FIG. 9, the side piece section 44 sandwiches aserpentine fin 46 against the endmost one of the tubes 28. Typically,this structure will be provided on both sides of the case. Additionalserpentine fins 46 extend between adjacent ones of the tubes 28 as well.

The foregoing description basically describes only a single quadrant ofa typical heat exchanger. Those skilled in the art will recognize that acomplete heat exchanger will include two of the header plates 20 thatare spaced in parallel with the tubes 28 running between the two headerplates 20 as mentioned previously. It will also include two of the tanks30, one for each header plate, and two of the side piece/end caps 40,one on each side of the heat exchanger for sandwiching one of the fins46 against the endmost tube 28 on each side of the heat exchanger.Further, as there will be two of the tanks 30, one assembled to each ofthe header plates 20, there will be a total of four of the end capsections 38, one for each end of each of the two tanks 30.

In the usual case, all of the components will be made of aluminum and,where required, provided with braze clad material, i.e., an aluminumbrazing alloy having a melting point somewhat less than the meltingpoint of the aluminum of which the components are formed. In some cases,the braze cladding will be on only one side of the component, while inother cases, it may be on both sides of the component. In some cases, acomponent may not be braze clad at all. By way of example, the tank 30must be joined to the end caps 38 as well as to the header plate flanges22. If braze cladding is located on the remote surfaces of the twoflanges 22, that is, the two that face away from each other, as well ason the innermost side of the side piece/end cap 40, then the tank 30 maybe free of braze cladding because braze cladding will always be presentat the interfaces of the header plate flanges 22 and the facing surfaceof the bent edge 36 of the end cap piece 38. In addition, this willresults in braze cladding being located on the inner side of the sidepiece section of the end cap/side piece structure 40 for bonding to theadjacent serpentine fin 46.

Turning now to FIGS. 1-4, four different forms of the end cap/side pieceassembly 40 will be described. In each case, each side piece section 44is formed integrally with two end cap sections 38, with there being oneend cap section 38 at each end of the side piece section 44. Twosections 38 and 44 are separated by one or more cutouts 50. In theembodiment of FIG. 1, cutouts 50 are separated by a single connectingstrand 52 which is located centrally of the side piece/end cap assembly40. In contrast, cutouts 54 are arranged to define two, off-centerconnecting strands 56 in the embodiment of FIG. 2.

FIG. 3 includes non-centered, multiple connecting strands 56 separatedby cutouts 54 like the embodiment of FIG. 2 while the embodiment of FIG.4 includes a single, central connecting strand 52 and cutouts 50 as inthe embodiment of FIG. 1.

In all cases, the side piece/end cap structures 40 are integrallyformed, that is, formed of a single piece of metal as by stamping. Theside piece sections 44 include flanges 60 that are directed toward theendmost tube on the corresponding side of the core and serve to confinethe serpentine fin 46 that is sandwiched against the endmost tube 28 bythe side piece section 44 to aid in assembly.

The embodiments of FIGS. 1 and 2 have identical end cap sections 38. Asmentioned previously, each end cap section 38 is surrounded on threesides by a bent edge 36 about which one end of a tank 30 is abutted tobe sealingly bonded thereto. As seen in FIGS. 1 and 2, integral,U-shaped clips 62 extend from the bent edge 36 away from the tank (seealso FIG. 8) with an outer leg 64 directed back toward the tank toresiliently clip on the end of the tank. This serves to fasten the tank30 to the end cap section 38 during brazing or soldering.

To facilitate fitting of the end of the tank 30 into the clips 62, asloped or slanted surface extension 66 extends away from the end capsection 38 and is located on one side of the leg 64 to serve as a pilotto guide the lower end of a corresponding side 34 of the tank 30 intothe proper location and retain it by the resilience of the material ofwhich the clip 62 is made.

Each of the embodiments of FIGS. 1 and 2 also includes, on the part 70of the bent edge 36 remote from the side piece section 44 adjacent thepart 70 of the bent side 36 a tab 72 which can be bent and deformed overthe wall 32 of the tank as best seen in FIG. 6. The tab 72 thus servesto hold the wall 32 in firm engagement with the surface 70 during thebrazing process to assure a leak-free joint.

An embodiment of the invention utilizing the side piece/end capassemblies 40 shown in FIGS. 3 and 4 is illustrated in FIGS. 11-14. Inthis case, U-shaped spring clips 80 are integrally formed on each end 82of each tank 39, and specifically the sidewalls 34 thereof. As seen inFIG. 13, each of the U-shaped clips 80 includes an outwardly flared orsloped surface for the clips 80 to allow them to be fitted to outwardprojections on both sides of each end cap section 38. That is, theflared sections 84 serve the same purpose, in the embodiment of FIGS.11-14 as the slope surfaces 66 of the clips 64 in the earlierillustrated embodiments using the assemblies 40 of FIGS. 1 and 2.

The tab 72 is retained in the embodiment of FIGS. 10-14.

It is to be particularly noted that connecting strands 52, 56, and thevarious embodiments typically may be such that there is a slight offsetof the end cap section 38 from the side piece section 44. As can beseen, for example, in FIGS. 5 and 9, it is not unusual for the sidepiece section 44 to be located outwardly of the end of the headeradjacent thereto, and the offset accommodates so locating the variouscomponents.

Importantly, the cutouts 50, 54 provide a weak spot at the point whereatthe side piece sections 44 would be connected directly to the header 20or connected via the connection to the end cap section 38 and ultimatelyto the header 20 through the tank 30. It is this area whereatsubstantial thermal stress can exist and is transmitted to the tube toheader joints. Because the connecting strands are relatively thin, ascan be seen in the drawings, they may readily fracture to relievethermal stresses as required. To achieve the desired relief in suchcircumstances, it is highly desirable that the cross-sectional area ofthe piece of metal of which each assembly 40 is formed be reduced by atleast 50% at the cutouts 50 or 54. Preferably, the cross sectionreduction is at least about 80%. The side of the reduction is measuredin a plane transverse to the length of each side piece/end cap assembly.

Moreover, ideally, the connecting strands 52, 56 are sized so that theymay easily be intentionally severed if desired, following brazing orsoldering. In fact, it is only necessary that the connecting strands 52,56 be of sufficient cross-sectional area as to provide some support forthe end cap sections on the side piece section 44 during pre-assemblyusing the clips 62, 80 and the tab 72 during pre-assembly prior tobrazing or soldering. Thus, it will be seen that the invention providesa heat exchanger that eliminates or minimizes thermal stresses at two ofthe header joints that may cause failure due to thermal cycling and/orthermal gradients. Furthermore, unique use of the clips and tabseliminates the need for special fixtures or jigs to hold the componentsmaking up the heat exchanger in assembled relation prior to soldering orbrazing, thereby minimizing the cost of fixturing during assembly.

1. A heat exchanger comprising: a pair of parallel headers each having spaced tube slots aligned with tube slots in the other header; tubes extending between aligned ones of the tube slots in said headers; fins extending between the tubes; side pieces on opposed sides of the heat exchanger embracing said fins thereat and extending substantially between corresponding ends of the headers; a pair of channel-like tanks, one for each header, fitted to the corresponding header oppositely of the tubes; and end caps having bent edges embracing and sealingly closing opposite ends of each said tank, said end caps being integral extensions of each end of each side piece to form end cap/side pieces and characterized by a reduction in cross section of each end cap/side piece adjacent each end of each header of at least about 50%, each defined by at least one cutout thereat.
 2. A heat exchanger comprising: a pair of parallel headers each having spaced tube slots aligned with tube slots in the other header; tubes extending between aligned ones of the tube slots in said headers; fins extending between the tubes; side pieces on opposed sides of the heat exchanger embracing said fins thereat and extending substantially between corresponding ends of the headers; a pair of channel-like tanks, one for each header, fitted to the corresponding header oppositely of the tubes; and end caps having bent edges embracing and sealingly closing opposite ends of each said tank, said end caps being integral extensions of each end of each side piece to form end cap/side pieces and characterized by a reduction in cross section of each end cap/side piece adjacent each end of each header of at least about 50%, each defined by at least one cutout thereat; and fasteners for securing said end caps to said tank ends during assembly of the heat exchanger.
 3. The heat exchanger of claim 2 wherein each said reduction is at least about 80% of said cross section and said end caps and side pieces remain integral about said cutout(s) through the retention of a connecting strand or a small number of connecting strands extending across said cutout(s) from the side piece to the integral end caps on each end of each side piece.
 4. The heat exchanger of claim 3 wherein said heat exchanger is formed of aluminum and is assembled by brazing, said connecting strands being sized to be readily severed if necessary.
 5. The heat exchanger of claim 2 wherein said fasteners include resilient U-shaped clips on said end cap bent edge or said ends of said tanks.
 6. The heat exchanger of claim 2 wherein said fasteners include a tab on each end cap bendable to overly and engage an adjacent end of said tank.
 7. The heat exchanger of claim 5 wherein said U-shaped clips each includes a sloped extremity on at least one of the legs thereon to serve as a pilot surface for receipt of a corresponding end of said tanks or a corresponding bent edge of said end caps.
 8. The heat exchanger of claim 2 wherein said cutout(s) defines a central connecting strand extending between each side piece and the associated end caps.
 9. The heat exchanger of claim 2 wherein said cutout(s) defines two spaced off center connecting strands extending between each side piece and the associated end caps. 